Web feeding means



Feb. 19, 1957 R. c. wxLcox WEB FEEDING MEANS Filed Sept. 30. 1955 4 SheetsnSlpeet 1 VA MM/tl .vnf m lkw {o/\ mc e. mm w fu /E WW n MM .5 J d. M 4 l Y M f j D n R o w. m Y m Smwm S R y, z R M4 ),R A f w W k Mm u a n vm Mn /MH 0 A v R Lw n f W o aw/w, nf H M rn `L m An A rf Z e 4k 4. 0K3 m il -..4| l a v f 4 wm, R im @am `V VMM wm f nv um n r m Ps )Pf I. WM D m w. wlwu vkvalb 111 I dwilf Feb. 1.9, 1957 R. c. wlLcox WEB FEEDING MEANS Filed sept. so, i955 4 Sheets-Sheet 2 INVENTR.

RUY E. INILCDX TTORN E Y Feb. 19, 1957 l R. c. wlLcox 2,782,355

WEB FEEDING MEANS Filed Sept. 50, 1955 4 Sheets-Sheet 5 IN VEN TOR.

REY E. WILEUX l BY ATTORNEY Feb. 19, 1957 R. c. wlLcox was FEEDING MEANS 4 Sheets-Sheetr 4 Filed Sepia. 30, 1955 INVENTOR. REY E. NILCUX TTKNY United States Patent O WEB FEEDING MEANS Roy C. Wilcox, Haddonlield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1955, Serial No. 537,786 9 Claims. (Cl. S18-602) This invention relates to web feeding means, and more particularly to a control system for establishing a predetermined rate of feeding such a web.

In the art relating to web feeding means, with particular attention to such web means `as magnetic record tape, efforts have been made to assure `that the web, or tape, will be fed past a transducing station at a constant predetermined velocity. ln accomplishing this, the tape is frequently driven by a capstan which is, in turn, driven by a suitable constant speed motor such as a synchronous motor. In order to assure a constancy and smoothness of the feeding of the tape, the motor shaft, or capstan shaft, carries a relatively large high inertia flywheel. The lflywheel serves to absorb or dampen any tendency of the shaft of the capstan to be driven with relatively rapid changes in velocity. With such an arrangement, diiiiculty is experienced in causing the ywheel, therefore, the capstan, to be brought up to the predetermined driving speed when initiating operation of the apparatus.

It is, accordingly, an object of the present invention to provide an improved speed control system for a web or tape driving means whereby maximum torque is applied to the driving motor during starting, `and signal responsive torque control means are applied as the mechanism approaches the desired velocity.

It is another object of lthis invention to provide a velocity control system for a web driving means as set forth wherein a driving motor is fully energized and the applied Atorque control comprises a signal controlled brake.

In accomplishing these and other objects, there has been provided, in accordance with the present invention, a capstan velocity control system wherein a capstan is adapted `to be driven by a suitable motor. A magnetic brake is coupled to the motor to control lthe torque thereof. A

velocity indicating control signal is obtained either from the web being driven or from a signal generating device associated with the motor or capstan shaft. The velocity indicating tone or signal is compared in phase and frequency wt-ih a standard reference signal. The comparison produces an error signal which is amplied and applied to control the operation of the magnetic brake. When the error signal is such as to indicate a substantial discrepancy between the desired velocity and the actual velocity, the frequency of the signal is too great to be significant in the operation of lthe brake. Means are provided for converting the rapidly fluctuating error signal into useful signals which may 'then be applied, in a proper sense, to control the operation of the aforesaid brake.

A better understanding of this invention may be had from the following detailed description when read in connection with the accompanying drawing in which:

Fig. l is a schematic block diagram of a control system constructed in accordance with the present invention;

Fig. 2 is a chart representative 4of the torque response that the capstan of the control system would manifest if the signals which would be derived from 2,782,355 Patented Feb. lg, i957 controlled solely by one portion of the control system;

Fig. 3 is a similar chart showing the torque response of the capstan if it were controlled solely by another part of the control system;

Fig. 4 is a chart showing the torque response of the capstan when yunder the combined control of the two portions of the system represented by the charts of Figs. 2 and 3;

Fig. 5 is a chart representing the actual applied Itorque of the capstan to the control of the system shown in Fig. l;

Figs. 6, 7 and S combine to show a circuit diagram illustrating a suitable circuit for carrying out -the invention; and

Fig. 9 is a diagram illustrating the arrangement of Figs. 6, 7 and 8 to form a complete circuit.

Referring now to the drawings in more detail, there is shown in Fig. l a capstan 2 about which there is positioned a web member 4 which may, for example, be a magneti-c record `tape having television signals recorded thereon. Positioned adjacent the capstan is a magnetic record pickup head 6 or other suitable signal detecting means. The capstan is mounted on a shaft 8, which, for purpose of convenience of illustration, is shown as being the shaft of a driving motor 10. ln actual practice, the motor shaft may be separate from the capstan shaft with suitable driving couplings connected therebetween. Also on the motor shaft S there isa magnetic brake i2. lFurther on the shaft 8, there is positioned a tone or signal generator 14 with a suitable signal detecting means i6. The motor I() is of the type which is known in the art as a hysteresis motor which is characterized in that it provides a substantially constant torque from zero speed up to a synchronous speed.

In the web `driving system, a motor normally runs at a speed which is slightly in excess of the desired capstan velocity. The magnetic brake 12 is then applied, under suitable controls, to slightly retard the velocity of `the motor. The control of the magnetic brake 12 is such that the motor velocity may be controlled, through operation of the brake, in a range of speeds slightly above and slightly below the predetermined desired velocity. The present invention is primarily concerned with `the obtaining and applying of suitable signals to the magnetic brake to etfect the desired control.

ln initiating the operation of the motor ld, the capstan 2 and the tone generator 14 are driven at increasing velocities until the desired speed is reached. As the tone generator 14 is rotated, a series of signals are -developed and detected by the detecting means, lo. These signals are indicative of the instantaneous rotational velocity of the motor 10 and, therefore, of the capstan 2. The signals from the detecting means i6 are applied through an amplifier 18 to a contact 2i) on a switch 22. When the switch is closed on the Contact 2G, the signals from the `amplilier are applied to a pulse Shaper 24 where the signals from the `tone generator 14 are formed into sharp narrow pulses of energy. These sharp narrow pulses are applied to a phase detector 26.

Also applied to the phase detect-or 26, from a source of reference signals represented by the terminal 28, is a `series of sawtooth wave signals. The frequency of the sawtooth wave signals corresponds to the frequency of the tone generator 14 if the motor were driving the capstan at exactly the desired velocity. The output of the phase discrimina- 'tor is essentially a low frequency sawtooth wave of reversible polarity and whose frequency is indicative ofthe extent of the discrepancy between the frequency of the signals derived from the tone generator M and the frequency 4of the reference signals. This signal is amplified ICC in an amplifier 3G, the output of which is applied yto energize the Imagnetic brake 12.

ln such driving systems, it is usual that a relatively heavy fiywheel is also mounted on the capstan shaft which flywheel absorbs rapid changes in applied torque and tends to smooth the operation of the capstan. If the signals applied from the phase detector 26 in the amplifier 3@ are of a relatively high frequency, then application of such signals to the brake would be fruitful of nothing. If, for example, there was a l cycle per second discrepancy in the frequency of the signals from the tone generator and the reference signals, then the frequency of the signals applied to the brake would similarly be l() cycles per second. Since this signal has an average value of zero (a portion of the signal being positive while the remainder is negative) the resultant effect on the brake and therefor on the capstan would be nullified and absorbed in the inertia of the ywheel.

In order to derive a usable signal from the output of the phase detector, the signal is fed through a differentiating circuit 32 to produce a series of pulses, the polarity of which is indicative of the direction of the discrepancy between the signals derived from the reference source and the tone source. The differentiated signals are applied through a rectifier 34 to an amplifier 36. The arnplificr 36 is connected to the amplifier 30 in such a manner as to control the operation of the amplifier 30, irrespective of what is fed to it from the phase detector 26. It will k'be appreciated, at this point, that, when the signals from the tone generator 14 and from the source of reference signals 28 bear a lsubstantially constant phase relationship, there will be no appreciable signal passing through the differentiator 32, the rectifier 34 and the amplifier 36. Under those conditions, the amplifier 30 is controlled by the output from the phase detector 26.

As the discrepancy between the frequency of the signals derived from the tone `generator and those derived from the reference source increases, the frequency of the signals generated by the phase detector increases accordingly. However, these signals have components of opposite polarity which increase in relative amplitude until eventually they overshadow the principal signal output and force the total output to reverse. When this condition occurs, the signals derived from the phase detector output, by means of the differentiator 32 and rectifier 34, no longer have significance when applied to the magnetic brake 12. When the signals from the phase detector are further increased in frequency, the resultant effect on the magnetic brake is rather erratic. When these signals from the differentiating circuit 32 and rectifier 34 are applied to the magnetic brake 12, the resultant capstan torque is substantially as shown or represented `by the curve of Fig. 2. The abscissa is representative of the frequency of the signals developed by the tone generator. Along this axis, fu represents the frequency of the signals from the tone generator which are of the same frequency as the signals derived from the source of reference signals. The ordinate of this curve is representative of the resultant capstan torque. This resultant capstan torque is the net driving torque applied to the shaft 8 and is the difference between the full motor torque and the braking force applied to oppose that full motor torque by the brake 12.

It will be recalled that the motor is normally operated, when no 'braking force is applied, at a speed which is slightly in excess of the ultimate desired speed. This is reduced to the desired speed by the application of a predetermined braking force applied from the brake 12. Thus, if the motor is tending to drive the system at a speed which is less than the desired speed, the signals applied from the differentiator and rectifier will be in a direction to reduce the braking force applied through the brake 12 to the motor 10, thereby increasing the resultant torque. However, this relationship holds only until the frequency relationship of the signals from the tone generator and those from the source of reference signals is such that the derived signal is of a polarity which produces the aforesaid decrease in the resultant torque.

In order to eliminate the effect of the undersirable results in the response of the brake and capstan motor, means are provided for effectively tilting the curve shown in Fig. 2 to arrive at a response characteristic which is represented by the curve of Fig. 4, This is achieved by superimposing on the foregoing circuits an additional circuit whose frequency response characteristic is such to to produce, when acting alone, a resultant capstan torque response curve such as that shown in Fig. 3. When clipped at a suitable clipping level before the frequency fo is reached the resultant output can be added to the curve of Fig. 2 to produce the curve of Fig. 4. The means for producing the results illustrated in Fig. 3 includes an integrating circuit 38 which is connected to the output of the pulse shaper 24. The integrator 38 is connected, through a cathode follower amplifier 40, to the amplifier 36. The output of the integrator 33, when amplified and applied to the amplifier 36, supplies a signal to the amplifier 36 which eliminates the undesirable effect noted with respect to Fig. 2 by effectively raising the dips in the response curve (Fig. 2) to a predetermined minimum level as shown in Fig. 4.

Thus far, the signals to be compared with the reference signals have been described as coming from the tone generator. It should also be noted that control signals may also be recorded on the tape 4. These signals may be detected by the pickup head 6 and applied, through an amplifier 42, to a frequency divider 44 and, from there, to a contact 46 on the switch 22. From the switch 22, the signal derived from the tape 4 is applied in the same manner as the signal derived from the tone generator to the pulse shaper thence to the phase detector 26 and/or the integrator 3S. In this manner, either the signals recorded on the tape or signals derived from the tone generator on the capstan shaft, both of which effectively indicate the velocity of the capstan, may be compared with the reference signals to provide control signals for controlling the operation of the magnetic brake 12.

An example of specific circuit means for carrying out the foregoing control is illustrated, schematically, in the circuit diagram of Figs. 6, 7 and 8. If, as suggested earlier in the description, the system is used to control the velocity of the magnetic record tape in a video recording system, the source of reference signals may comprise a generator which supplies synchronizing signals for the television system. These reference signals would appear as pulses of energy which are applied to an input terminal 48. From the terminal 48, the signals are applied to an amplifier 5f). The amplified signals from the amplifier 50 are applied to a discharge tube 52. The discharge tube S2 is connected in parallel with the capacitor 54. The discharge tube is normally biased to cut off. When this tube is thus cut off, the capacitor 54 is charged from the high voltage .source 56 through a series of resistors 58, 60, 62. Whenever the discharge tube 52 is pulsed into heavy conduction the capacitor 54 is discharged. This arrangement produces a sawtooth voltage which is applied to the control grid of each of the amplifier tubes 64, 66. These amplifiers 64 and 66 are connected in parallel. Suitable feedback circuitry is provided between the amplifier tube 64 and the charging resistor 62 by the cathode circuit of the amplifier tubes 64 and 66 to provide a constant current source for capacitor 52.

The resultant sawtooth signal is applied, through a lead 68 to a phase detector 26 which comprises a diode bridge in which four diodes 70, 72, 74 and 76 are arranged respectively in the four legs of a bridge circuit. The signal input is fed to one corner of the bridge circuit and the signal output of the bridge circuit is connected to the diagonally opposite corner thereof. The other two opposing corners of the bridge circuit are connected together by a path which includes the secondary of a coupling transformer 78 the primary of which is coupled to a pulse shaping amplifier 24.

Signals from the tone generator 14 (see Fig, l) are applied to the terminals @il of the amplifier 18. The signals applied from the tone generator to the amplifier i8 may be in the form of sine waves. The sine waves are applied to an .overdriven amplifier tube 82 which provides a measure of clipping of the waves. These clipped waves are differentiated in a differentiator circuit ineluding a capacitor Se and the resistors 86 and 88. The dif` erentiated signals are applied to a second amplifier tube 9% and, from there, to monostable multivibrator including the tubes 92 and 94. The monostable multivibrator is triggered by the differentiated signals and produces a series of narrow pulse signals at a rate corresponding to the frequency of the signals developed by the tone generator. The pulse signals from the multivibrator are applied to the contact 20 of the switch 22.

The switch 22, when closed on the Contact Ztl, applies the pulse signals from the multivibrator to the pulse shaping amplifier 24 as represented by n first amplifier stage 96 and a second amplifier stage 95. The output of the second stage 98 is coupled to the transformer 7S in the phase detector 26. This coupling multiplies the signal derived from the tone generator 14 by the signals from the source of reference signals 2.8 in a manner to produce an output product signal which is indicative of the phase relationship of the signals from the two sources. The pulse signals derived from the tone generator produce a bias voltage across the parallel connected capacitor 2lb@ and resistor 3h32 in the bridge circuit. voltage is sufficient to maintain all four diodes in cutoff condition until such time as one of the narrow pulses derived from the tone generator 14 occurs. Such pulse triggers on the four diodes, momentarily. During the instant that the diodes are rendered conductive, a potential difference relationship may exist between a storage capacitor lid-i in the output circuit of the bridge and the output of the amplifiers 6d and 66. The potential difference will depend upon the phase position of the sawtooth voltage applied from the amplifiers 64 and 66 at the moment when the diodes are turned on. lf the charge on the capacitor lfll is greater than the instantaneous potential of the sawtooth voltage applied to the bridge, then the capacitor will be partially discharged,

during the conduction of the diodes, to a voltage level f which is commensurate with the instantaneous Voltage of the sawtooth wave. Conversely, if the charge on the capacitor is less than the instantaneous voltage of the sawtooth wave, then additional charge will be applied to the capacitor lud during the time of the conduction f of the'diodes. It may be seen that a phase difference in the occurrence of the pulses from the tone generator with respect to the reference signal will produce a generally sawtooth type signal as a result of the charging condition of the capacitor lllll. The frequency of 'this latter sawtooth signal will be substantially equal to the difference in the frequency of the two sources of signals. lf the tone generator signals are of a frequency which is greater than the frequency of the reference signals, then the output signal from the phase detector will be a sawtooth wave which has a relatively long fall time and a short rise time. On the other hand, if the frequency of the signals from the tone generator is less than the frequency of the signals from the reference source then the output signal from the phase detector will be sawtooth wave which has a relatively slow rise time and a fast fall time. These signals from the phase detector 2J are applied to the amplifier 3f). This amplifier 3b includes the first stage or cathode follower amplifier iil and a second stage amplifier 10S which is coupled to the This bias cathode follower amplifier L106 through a potentiometer llt). The potentiometer may be adjusted to determine the overall gain of the amplifier. The output of the amplifier 10S is applied to a third and a fourth stage i amplifier i12 and lid, respectively, then to parallel power amplifiers 116 and lid. The .output of the power amplifiers is fed to a coil l2() which is the energizing coil of the magnetic brake l2.

The output of the cathode follower amplifier lilo is also applied to a differentiating circuit 32. This differentiating circuit includes an amplifier 122 and a resistance-capacitance differentiator comprising the capacitor 24 and a resistor 126. Also included in the diferentiating circuit is an amplifier stage 123 for the differentiated signals. lt will be recalled that the signals developed by the phase detector comprise a sawtooth wave which had a slow rise time and a fast fall time if the signals from the tone generator were of a lower frequency than the signals 'from the reference source. Similarly, if the signals from the tone generator were of a higher frequency than the signals from the reference source, then the derived signal will be a sawtooth wave which had a slow fall time and a sharp rise time. This signal, when differentiated in the differentiating circuit 32, produces a negative pulse when the tone generator' signals are of a lower frequency than that of the reference signals; and a positive pulse when the tone wheel signals are of a higher frequency than that of the reference signals. These pulses are applied to a bipolar rectifier which includes a pair of diodes lfl and i3-Z and a pair of capacitors i3d and i3d. The capacitor i3d is con ected between the anode of the diode 13d and the cathode of the diode i312. The other capacitor E36 is connected between the cathode of the diode E32 and ground. Each of' the capacitors 34 and l36 has a shunt connected resistor '.d and 140, respectively. When a negative pulse is applied to the rectifier 3d, the diode i3d becomes conductive, applying a negative charge to the capacitor 134i. 'lhis negative charge is applied to the control grid of the cathode follower amplifier 3d. The amplifier 3d comprises an override amplifier which, whenever a signal is applied to cause conduction thereof, applies a control signal to the control grids of the two amplifiers ll and im. This control signal controls the operation of the amplifiers H6 liti, irrespective of any signals applied directly from the phase detector 26 because of the .isolation afforded by a resistor lidi in the anode circuit of the amplifier tube lift. The application of the negative pulse to the control grid of the amplifier 36 reduces the conduction thereof. This applies a negative signal to the control grids of the power plifiers H6 and li-S reducing the braking current applied to the coil E21? of the brake l2. Reduction of this braking force allows the motor to increase in velocity to establish a synchronous condition of the tone generator signals with those of the reference source. On the other hand, the application of a positive signal pulse to the rectifier 34 causes conduction of the diode lSZ. rfhis applies a relatively positive charge to the capacitor This positive charge is applied to the control grid of the amplifier 36 increasing the conduction thereof. This increases the current flowing through the brake coil 12A? and causes the brake to retard the overspeeding motor.

As previously noted, when the frequency of the signals fro n the phase detector is high, due to the tone generator being driven at a speed to produce signals which are considerably lower in frequency than the frequency of the reference signals, the response of the differentiator and rectifier becomes erratic as shown in the curve of Fig. 2. In order to overcome this undesired effect, a portion of the signal from the pulse shaping amplifier 2d is used to control the operation of the override amplifier 36. T he signal from the pulse shaping amplifier 24 is obtained from the output of the first stage 96 thereof. rThis is fed to the control grid of a vacuum tube 142. This tube is normally biased to cutoff. The output of the tube 142 is coupled to the control grid of a second tube 144 which is connected to be normally conducting. The output of the second tube 144 is applied, through a voltage regulator 146, to the cathode follower amplifier 148. The output of the cathode follower amplifier is connected to the cathodes of a pair of diodes 150. The anodes of the diodes 150 are connected in the grid circuit of the override amplifier 36. In thi-s arrangement, whenever the first tube 142 is in a nonconducting state, the second tube is coupled to be highly conductive. The conduction of the second tube 144 renders the voltage regulator less conductive, therefore, the cathode follower 148 is also conditioned to bc nonconductive. This puts a rather large negative potential on the cathodes of the diodes 150 conditioning them to be conductive whenever a signal appears at the anodes thereof. In this condition, signals which would have been applied to the grid of the override amplifier 36 are bled off or shunted away from the grid of the amplifier 36. This constitutes means for deactivating the override amplifier which maintains the power amplifiers 116 and 118 in a minimum conduction or cutoff state. Thus, when the signals from the tone generator are below a predetermined frequency, substantially no current is applied to the coil 120, leaving the brake 12 deenergized. In this condition, the full driving torque is applied to the motor and the motor is permitted to attempt to bring the driving system up tothe desired speed.

When a pulse of energy is applied to the control grid of the first tube 142, that tube is rendered 4momentarily conductive. However, the conductive status of the second tube 144 is maintained by a storage Capacitor 152 coupled between the anode circuit of the first tube 142 and gro-und. This relationship holds until such time as the frequency of thc pulses from the pulse shaping amplifier increases to a predetermined desired frequency. The frequency of these pulses is, of course, determined by the frequency of the signals derived from the tone generator 14. When the frequency of these pulses has increased to the desired predetermined frequency, which may be that frequency represented by the vertical dashed line in Figs. 2, 3, 4 and 5, tne conduction of the first tube causes a reduction in the conductivity of the second tube 144. This increases the voltage applied to the voltage regulator 146, rendering that tube conductive. The conduction of the voltage regulator 146, in turn, causes the cathode follower amplifier 148 to become conductive, raising the potential on thc cathode of the diodes 15G, rendering those diodes nonconductivc. When the diodes 150 bccomc nonconductive, then signals applied to the grid o-f the override amplifier 36 exercise the desired control over the operation of the brake 12. Thus, in Fig. 3, the horizontal dashed line, which intersects the curve at the point where the previously mentioned vertical line intersects the curve, represents the level below which the integrating circuit has no effect on the control of the brake 12.

in Fig. 4 the composite curve is shown being intersected by a horizontal dotted line. This line represents the capstan motor torque when no braking effort is applied from the brake 12. ln view of this arrangement, it is apparent that the control that the brake exercises upon the operation of the motor is not applied until the motor approaches the immediate vicinity of the desired velocity. This net driving effort is shown in Fig. 5 in which the motor torque is constant up to the vicinity of the desired control velocity. On this diagram, there is shown a vertical line labelled fmax. This is the maximum frequency of the tone generator signals and is determined by the maximum velocity attainable by the synchronous motor.

it will be recalled that control ysignals may be obtained from the record member being driven as well as from a tone generator coupled to the motor shaft. In this illustrated example, i. e., that of recording television signals on magnetic record tape, television synchronizing pulses are recorded along with the picture information. In conventional practice, the television synchronizing signals occur at a rate of 15,750 C. P. S. The reference signal is chosen at 1/6 of this value or 2,625 C. P. S. The signal derived from the tape must be subdivided to provide a signal which is on the same order of frequency as thc reference signal. Therefore, the signals from the tape are rectified and the positive peaks of the signal are applied to the amplifier 42 a first stage of which is amplifier tube 154. The output of the amplifier 154 is differentiated and applied to a second stage amplifier' 156. The pulse output of the second stage amplifier is applied to trigger the monostable multivibrator 44 which includes tubes 153 and 160. The monostable multivibrator is biased to provide a repetition rate which is on the order of 2,625 C. i). S. This multivibrator then comprises a 6-count frequency divider. The output of this multivibrator 4i is applied to the Contact 46 of the switch 22 from which it is fed to the pulse shaping amplifier 24, as was the signal from the tone generator 14. in this manner, the capstan motor 10 can be controlled to pro vide synchronization between a reference signal and a control signal derived either from the motion of thc tape being driven or from a tone generator associated with the mechanical drive system. When the velocity of the tape or capstan has been brought into the range of velocities represented by the fiat portion of the curve in the vicinity of fo in Fig. 5, the override amplifier 36 is stabilized with no signal on the control grid thereof. in this condition the override amplifier exercises no further control over the power amplifiers 116 and 118. This allows the brake to be controlled by the signals from the amplifier 3ft. ln this narrow range the frequency of the signals is low enough to permit the drive system to be responsive thereto. This will permit the drive system to be operated at such a velocity that the frequency discrepancy is substantially zero and phase error is maintained at a minimum.

Thus there has been provided an improved speed control system for a web or tape driving means wherein signal responsive torque control means are applied to control the operation of the driving means in the vicinity of a desired controlled velocity.

What is claimed is:

l. A control means for a web feeding system, said control means comprising a capstan for driving a web member, means for rotationally driving said capstan, means for producing a signal indicative of the rotational velocity of Said capstan, a source of reference signal, means for comparing said reference signal and said signal indicative of said velocity, said comparing means being responsive to said two sets of Signals to produce a signal indicative of a frequency discrepancy of said velocity indicating signal with respect to said reference signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said signal from said comparing means to said torque control member, means responsive to signals from said comparing means for producing signals indicative of the direction of the frequency discrepancy between signals from said source and said velocity indicating signals, and means for applying said direction indicating signal to said torque control member.

2. A control means for a web feeding system, said control means comprising a capstan for driving a web member, means for rotationally driving said capstan, means for producing a signal indicative of the rotational velocity of said capstan, a source of reference signals. means for comparing said reference signals and said signals indicative of said velocity, said comparing means being responsive to said two sets of signals to produce a signal indicative of a frequency discrepancy of said velocity indicating signal with respect to said reference signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said signal from said comparing means to said torque control member, differentiating means coupled to said comparing means for producing signals indicative of the direction of the frequency discrepancy between signals from said source and said velocity indicating signals, and means for applying said direction indicating signal to said torque control member.

3. A control means for a web feeding system, said control means comprising a capstan for driving a web member, means for rotationally driving said capstan, means for producing a signal indicative of the rotational velocity of said capstan, a source of reference signals, means for comparing said reference signals and said signals indicative of said velocity, said comparing means being responsive to said two sets of signals to produce a signal indicative of a frequency discrepancy of said velocity indicating signal with respect to said reference signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said signal from said comparing means to said torque control member, differentiating means coupled to said comparing means for producing signals indicative of the direction of the frequency discrepancy between signals from said source and said velocity indicating signals, and means including a rectification circuit for applying said direc* tion indicating signal to said torque control member.

4. A control means for a web feeding system, said control means comprising a capstan for driving a web member, means for rotationally driving said capstan, said control means comprising means for producing a signal indicative of the rotational velocity of said capstan, a source of reference signals, a phase detector circuit, means for applying said reference signals and said velocity indicating signals to said phase detector, means inducing said phase detector for producing a signal indicative of a frequency discrepancy between said reference signals and said velocity indicating signals, a signal responsive torque control member coupled to said capstan driving means, means for applying said frequency discrepancy indicating signal to said torque control member, means responsive to signals from said phase detector for producing signals indicative of the direction of the frequency discrepancy between signals from said source and said velocity indicating signals, and means for applying said direction indicating signals to said torque control member.

5. A control means for a web feeding system having a capstan for driving a web member and a means for rotationally driving said capstan, said control means comprising means for producing a signal indicative of the rotational velocity of said capstan, a vsource of reference signals, a phase detector circuit, means for applying said reference signals and said velocity indicating signals to said phase detector, means including said phase detector for producing a signal indicative of a frequency discrepancy between said velocity indicating signal and said reference signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said frequency discrepancy indicating signals to said torque control member, a signal differentiating circuit coupled to said phase detector to produce signals indicative of the direction of the frequency discrepancy between said velocity indicating signals and said reference signals, and means for applying said direction indicating circuit to said torque control member.

6. A control means for a web feeding system having a capstan for driving a web member and means for rotationally driving said capstan, said control means comprising a tone generator coupled to said capstan for producing a signal indicative of the rotational velocity of said capstan, a source of reference signals, a phase detector circuit, means for applying said reference signals to said phase detector circuit, means including a pulse shaping circuit for applying said velocity indicating signals to said phase detector circuit, means including said phase detector circuit for producing a signal indicative of a frequency discrepancy between said reference signal and said velocity indicating signals, a signal responsive torque control member coupled to said capstan driving means, means for applying said frequency discrepancy indicating signal to said torque control member, means including a signal differentiating circuit coupled to said phase detector to produce a signal indicative of the direction of the frequency discrepancy between said reference signal and said velocity indicating signal, and means for applying said direction indicating signal to said torque control member.

7. A control circuit for a web feeding system having a capstan for driving a web member and means for rotationally driving said capstan, said control means including a tone generator coupled to said capstan for producing a signal indicative of the rotational velocity of said capstan, a source of reference signals, a phase detector circuit including a signal storage means, means for applying said reference signal to said phase detector, means including a pulse shaping circuit for applying said velocity indicating signals to said phase detector circuit, means including said phase detector circuit for producing a signal indicative of a frequency discrepancy between said reference signal and said velocity indicating signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said frequency discrepancy indicating signal to said torque control member, means including a signal differentiating circuit coupled to said phase detector to produce signals indicative of the direction of the frequency discrepancy between said reference signal and said velocity indicating signal, means for applying said direction indicating signal to said torque control member, and signal responsive means for deactivating said means for applying said direction indicating signal when said velocity indicating signal is of less than a predetermined frequency.

8. A control circuit for a web feeding circuit in accordance with claim 7 wherein said means for deactivating said means for applying said direction indicating signal includes a signal integrating circuit coupled to said pulse shaping circuit, shunt means controlled by the output of said integrating circuit, said shunt means being coupled to said direction indicating signal applying means to shunt said direction indicating signals away from said applying means.

9. A control means for a web feeding system having a capstan for driving a web member and means for rotationally driving said capstan, said control means comprising means for deriving synchronizing signals from said web member, a source of reference signals, a phase detector circuit, means for applying said reference signals to said phase detector circuit, means including a pulse shaping circuit for applying said synchronizing signals to said phase detector circuit, means including said phase detector circuit for producing a signal indicative of a frequency discrepancy between said reference signals and said velocity indicating signal, a signal responsive torque control member coupled to said capstan driving means, means for applying said frequency discrepancy indicating signal to said torque control member, means including a signal differentiating circuit coupled to said phase detector to produce a signal indicative of the direction of the frequency discrepancy between said reference signals and said synchronizing signals, and means for applying said direction indicating signals to said torque control member.

No references cited. 

